The IMGC volume-density standards for the Avogadro constant

Within the project for the determination of the Avogadro constant, the IMGC has developed volume-density standards in the form of single-crystal silicon spheres. In addition to a first sphere previously characterised and intercompared with a similar artifact, a new sphere of nearly perfect form is now available. The absolute determination of its mass and volume is presented together with the expected improvements in the assignment of a density value to high-purity and near-perfect silicon single-crystals.<>